EVAL-AD7656CB View Datasheet(PDF) - Analog Devices
Part Name
Description
MFG CO.
'EVAL-AD7656CB' PDF : 25 Pages View PDF
AD7656/AD7657/AD7658
Data Sheet
Software Selection of ADCs
The H/S SEL pin determines the source of the combination of
ADCs that are to be simultaneously sampled. When the H/S SEL
pin is logic low, the combination of channels to be simultaneously
sampled is determined by the CONVST A, CONVST B, and
CONVST C pins. When the H/S SEL pin is logic high, the
combination of channels selected for simultaneous sampling is
determined by the contents of the Control Register DB15 to
Control Register DB13. In this mode, a write to the control
register is necessary.
The control register is an 8-bit write-only register. Data is written
to this register using the CS and WR pins and the DB[15:8] data
pins (see Figure 29). The control register is shown in Table 10.
To select an ADC pair to be simultaneously sampled, set the
corresponding data line high during the write operation.
The AD7656/AD7657/AD7658 control register allows
individual ranges to be programmed on each ADC pair.
DB12 to DB10 in the control register are used to program
the range on each ADC pair.
After a reset occurs on the AD7656/AD7657/AD7658, the
control register contains all zeros.
The CONVST A signal is used to initiate a simultaneous
conversion on the combination of channels selected via the
control register. The CONVST B and CONVST C signals can
be tied low when operating in software mode (H/S SEL = 1).
The number of read pulses required depends on the number
of ADCs selected in the control register and on whether the
devices are operating in word or byte mode. The conversion
results are output in ascending order.
During the write operation, Data Bus Bit DB15 to Bit DB8 are
bidirectional and become inputs to the control register when
RD is logic high and CS and WR are logic low. The logic state
on DB15 through DB8 is latched into the control register when
WR goes logic high.
Table 10. Control Register Bit Function Descriptions
(Default All 0s)
DB15 DB14 DB13 DB12 DB11 DB10 DB9
VC VB VA RNGC RNGB RNGA REFEN
DB8
REFBUF
Table 11.
Bit Mnemonic
DB15 VC
DB14 VB
DB13 VA
DB12 RNGC
DB11 RNGB
DB10 RNGA
DB9 REFEN
DB8 REFBUF
Comment
This bit is used to select Analog Inputs V5
and V6 for the next conversion.
When this bit = 1, V5 and V6 are
simultaneously converted on the
next CONVST A rising edge.
This bit is used to select Analog Inputs
V3 and V4 for the next conversion.
When this bit = 1, V3 and V4 are
simultaneously converted on the
next CONVST A rising edge.
This bit is used to select Analog Inputs
V1 and V2 for the next conversion.
When this bit = 1, V1 and V2 are
simultaneously converted on the
next CONVST A rising edge.
This bit is used to select the analog input
range for Analog Inputs V5 and V6.
When this bit = 1, the ±2 × VREF mode is
selected for the next conversion.
When this bit = 0, the ±4 × VREF mode is
selected for the next conversion.
This bit is used to select the analog input
range for Analog Inputs V3 and V4.
When this bit = 1, the ±2 × VREF mode is
selected for the next conversion.
When this bit = 0, the ±4 × VREF mode is
selected for the next conversion.
This bit is used to select the analog input
range for Analog Inputs V1 and V2.
When this bit = 1, the ±2 × VREF mode is
selected for the next conversion.
When this bit = 0, the ±4 × VREF mode is
selected for the next conversion.
This bit is used to select the internal
reference or an external reference.
When this bit = 0, the external reference
mode is selected. When this bit = 1, the
internal reference is selected.
This bit is used to select between using the
internal reference buffers and choosing
to bypass these reference buffers.
When this bit = 0, the internal reference
buffers are enabled and decoupling is
required on the REFCAP pins. When this
bit = 1, the internal reference buffers are
disabled and a buffered reference should
be applied to the REFCAP pins.
CS
WR
t12
DB15 TO DB8
t11
t13
t15
t14
DATA
Figure 29. Parallel Interface—Write Cycle for Word Mode (W/B= 0)
Rev. D | Page 24 of 32
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